My creative process often starts with sketches of the rough composition to get the concept of the project down. Then I later move onto drawing each component in separate layers in order to be able to move them around to find the best composition.  As for the coloring part, what works best for me is to have different versions to compare in order to pick the one that best convey the tone of the project. Pantone chart helps me picture how the colors will look like on a physical product compare to on the screens.